The invention relates to a clamping toolholder, which comprises a shank with a recess for the support of a base plate and a disposable insert of the pin-type and also a clamping mechanism which includes a bushing, retained in a shank bore below the recess, and a clamping element having one part extending into the bushing and another part into the insert hole, so that the clamping element is supported within the bushing and is movable in the direction of the axis in a manner such that the movement is against forces preferably caused by cup springs.
A plurality of clamping systems are known. According to one approach, the pin-type inserts are clamped against one or several side walls of the shank recess by a clamp element that extends into the insert hole. The plate clamping takes place, for instance, by the turning of an eccentric pin or a pin system, consisting of one or several parts movable against one another. In other toolholder systems the clamping of a disposable insert takes place by a tipping of the pin, for instance, by an elbow lever system.
In toolholders with an eccentric pin, it is perceived as disadvantageous that the pin system has to be prepared very precisely. Because great forces have to be transmitted on the shank, the system must have a precise leading in the bore of the toolshank and needs great height in construction. Additionally, the tolerances of the dimensions of disposable inserts have to be small to guarantee a satsifactory clamping. Eccentric pins are regularly twisted by a hexagonal, hollow, socket, which causes problems in the use of the system. The hexagonal socket in the pin is often contaminated or blocked by chips. Preferably, in cases of small socket dimensions, a considerable abrasion by radiusing of the hexagon is given, which entails an overflow of the socket.
Clamping toolholders, with a pin tilting system are expensive to construct and produce. To obtain a sufficient clamping effect by tipping, the three distinguished equipment points for clamping, for instance in an elbow lever, should be located far away from each other.
Due to this remarkable bending, strains result in the clamping system. Also, in this case a satisfactory clamping with precise positioning of the inserts can be obtained only by very precise fabrication to guarantee that the predetermined equipment points of the elbow lever lie close to the cutting insert and recess of the shank.
It is known that the clamping of a cutting insert depends upon the established moment of rotation by the operator. This has a disadvantageous effect on the pin-type clamping with eccentric stud on the end because every established moment of rotation causes the end position of the eccentric to be different. For this reason, the clamping often does not occur in the predetermined direction.
In the past, clamping systems with cup springs have been prescribed, which render a clamping action, uneffected by the operator. According to such a construction, a bushing is screwed into a bore in the shank below the insert. Inside the bushing is a pin, which can be stretched by cup springs in the direction of the axis. The clamping of the cutting insert occurs with the pin through a system of levers which cause the pin to rest with one point at the inner wall of the insert hole and with two points at the screwed bushing. Even with that clamping arrangement one cannot warrant a precise clamping. Additionally, the height of construction is comparatively great, due to the arrangement of the three-point-support on top of the spring seating.